1. Field of the Invention
This invention relates to filled organic elastomeric matrixes and to coupling compositions added to the filler-organic elastomeric matrix for conserving or enhancing the physical and electrical properties of the filled organic elastomeric matrix. The invention more particularly relates to novel coupling compositions for addition to filler-organic elastomer blends for providing curable compositions having special application as insulation coatings for electrical cables upon curing with organic peroxides. The invention also relates to curable compositions containing the filler, organic elastomer, peroxide and coupling composition and to cured compositions resulting therefrom. The invention also relates to electrical cables provided with such cured compositions and methods for making same.
2. Description of the Prior Art
A substantial amount of research has been performed heretofore in connection with the treatment of fillers or reinforcing agents for the purpose of improving physical or mechanical properties of plastics, resins or rubbers reinforced with the filler. Much of this research has centered on the pretreatment of glass fiber reinforcement materials for resins and rubbers. For example, U.S. Pat. No. 3,702,783 describes the application as a size to glass fibers of a blend of 3-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane. U.S. Pat. No. 3,816,235 discloses a size composition for the treatment of glass fibers wherein the size composition contains a blend of aminoalkyltriethoxysilane and methyltriethoxysilane. U.S. Pat. No. 3,944,707 discloses the use as a size for glass fiber reinforcement for plastics, blends of vinyl silane or vinyl siloxanes and a beta-haloalkoxysilane. Similarly, U.S. Pat. No. 3,993,837 discloses glass fiber size compositions containing blends of epoxyalkylsilane or siloxane and a beta-haloalkoxysilane.
U.S. Pat. No. 4,049,865 discloses glass fiber size compositions containing a blend of an aminoalkylsilane and a vinyl silane. U.S. Pat. No. 4,130,677 discloses the sizing of glass bottle surfaces with am aminoalkylsilane. None of these patents disclose or remotely suggest the use of blends of an ethylenically unsaturated silane having at least 1 silicon bonded hydroxy or alkoxy group and an organosiloxane oligomer having at least one silicon bonded hydroxy or alkoxy group reactive with the inorganic substrate as an integral coupling composition for improving mechanical and electrical properties by mixing with an organic elastomer, a filler and peroxide followed by curing.
Martens et al U.S. Pat. No. 3,148,169 discloses the pretreatment of clay filler with a silicone fluid to coat the clay particles to impart a hydrophobic character to the clay and to mask the acidic nature of the clay so that peroxides later used as crosslinking agents are not deactivated.
Rykowski U.S. Pat. No. 4,179,537 discloses blends of an organofunctional silane, e.g., vinyltrialkoxysilanes, methacryloxyalkyltrialkoxysilanes, vinyltrihalosilanes and the like with a non-organofunctional silane, e.g., alkyltrialkoxysilanes, and the incorporation of such blends into organic resins, e.g., EPDM rubber for improving the adhesion between inorganic substrates such as clay fillers and the resin. This patent fails to disclose, teach or suggest the incorporation of siloxane oligomers in the coupling composition and suggests that the presence of siloxane oligomers in the resin-filler system could have a detrimental effect on coupling efficiency (col. 4, lines 54-63).
The Rykowski patent teaches the use of blends containing silanes having silicon-bonded 2-methoxyethoxy groups, e.g., vinyl-tris(2-methoxyethoxy)silane (Col. 2, lines 44-47), which releases 2-methoxyethanol as a hydrolysis by-product during use. The possible teratogenic properties of 2-methoxyethanol are currently under study indicating a potentially unacceptable risk in using vinyl-tris(2-methoxyethoxy)silane or similar materials as coupling agents or as components of coupling compositions.
Vinyl-tris(2-methoxyethoxy)silane, has been used industrially for many years as a coupling additive in mineral-filled EPM and EPDM wire and cable insulations. EPM is an ASTM designation for copolymers of ethylene and propylene; EPDM is a terpolymer of ethylene, propylene and a diene monomer such as ethylidene nor-bornene or 1,4 hexadiene. Vinyl-tris(2-methoxyethoxy)silane has been extensively used heretofore because it provides a unique balance of elastomer reinforcement and the degree of wet electrical stability required. It releases 2-methoxyethanol as a hydrolysis by-product when it is used and, unfortunately, 2-methoxy ethanol is now being studied as a suspected teratogen.
Vinyl-tris(2-methoxyethoxy)silane provided such a unique combination of high elastomer reinforcement, i.e., high degree of mechanical properties, and high degree of wet electrical stability, that it became the industry standard. No other single polymerizable, hydrolyzable silane has been found that can provide comparable performance on a one for one replacement basis. Many such other silanes provide acceptable electrical stability but fail to provide mechanical properties that are acceptable in every respect; notably as judged by 300% modulus which varies significantly with the other silanes.
None of the prior art references identified above discusses or suggests any compositions containing a blend comprising an organofunctional silane polymerizable with an organic elastomeric matrix and reactive with an inorganic substrate filler and an organosiloxane oligomer reactive with the inorganic substrate filler that is capable of providing mechanical properties and wet electrical stability properties comparable to the heretofore industry standard, vinyl-tris(2-methoxyethoxy)silanes.